IFAL: Issue First Activate Later Certificates for V2X

This paper presents IFAL, a provably secure and privacy conscious scheme for Vehicle-to-Vehicle and Vehicle-to-Infrastructure (V2X) communication. Issue First Activate Later (IFAL) is a practical and secure improvement to the leading European candidate for V2X (ETSI) and one that also merits over the leading US standard. IFAL incorporates a novel cryptographic mechanism that both avoids the need for certificate revocation and which supports vehicles with limited and intermittent connectivity. We introduce a new construction that is equivalent to symmetric key diversification in the public key setting with short, time-delayed activation. We also present a new formalisation of V2X security and privacy which we apply to IFAL to show that it is a provably secure and privacy conscious V2X scheme. IFAL is ETSI compliant and ready for integration into the standard.